1. Field of the Invention
The invention relates in general to thread wear gauges, and, in particular, to thread wear gauges for user with coil threads.
2. Description of the Prior Art
Coil threads, sometimes known as “wire threads”, are well known and widely used. See for example, Guard, U.S. Pat. No. 123,823, Gordon U.S. Pat. No. 1,311,646, Ballou U.S. Pat. No. 3,195,278, Strong U.S. Pat. No. 3,456,547, Hauser U.S. Pat. No. 3,945,070, and Gutshall U.S. Pat. No. 4,309,135. Coil threads are typically used in heavy duty construction applications where dirt, corrosion, and lack of lubrication cause substantial thread wear. In general, coil threads are not used in precision machine applications. Female coil threads, in the form of a coil of wire, are often cast into concrete where grit and a corrosive environment are inherently present. Threads with a coil thread profile are often used in other heavy construction equipment, such as steel street plates, and the like. Coil threads are very robust, and capable of functioning safely within a wide range of tolerances. Also, they remain functional even when the wear is uneven. Eventually, however, coil threads do wear out. When a coil thread in a piece of construction material, such as a steel street or road plate, becomes damaged to the point where it will no longer support the load for which it is rated, a serious safety problem may arise. Because coil threads remain functional throughout a wide range of tolerances, and the wear is frequently uneven, determining when a coil thread is too worn to be safe had been problematic, at least out in the field where it is impractical to use sophisticated testing equipment. Various thread gauges had previously been proposed, particularly as applied to machine screw threads. See, for example, Palm U.S. Pat. No. Des. 421,575 (a plate with male and female threads), Foster U.S. Pat. No. 2,662,300 (torque controlled go no-go plug gauge), Larsen U.S. Pat. No. 4,519,144 (a go no-go plug gauge with depth measuring capabilities), Van Horssen U.S. Pat. No. 4,724,618 (driver for a conventional plug gauge), Nelson U.S. Pat. No. 5,490,333 (adjustable three point roller thread ring gauge for external threads), Galestien U.S. Pat. No. 6,289,595 (machine for scanning a thread profile to determine thread geometry). The workers in this field had recognized the need for a simple, quick, and reliable way of determining when a coil thread, either male or female, has become worn beyond a safe limit.
These and other difficulties of the prior art have been overcome according to the present invention.